Contoured or fitted bed sheets are typically made from either woven fabric or knitted fabric. Contoured fitted sheets made from woven fabric generally have no inherent ability to stretch and grab around the mattress and so are often finished with an elastic binding around the bottom edge of the sheet to assist in holding the sheet to the mattress. The elastic binding presents problems, especially in the hospitality and healthcare markets where they are handled in commercial laundry environments. The harsh laundering processes involved tends to shorten the life of the elastic thereby limiting the service life of the sheet. Further, each sheet is typically fitted to a mattress having a thickness related to the sidewall depth or height of the sheet, especially at the corners. But, there is little uniformity to mattress thicknesses across styles or manufacturers creating particular problems in facilities that have a lot of beds, as typical of health care facilities and hospitality properties. Additionally, some beds, especially in the health care environment, are adjustable. Non-stretchable woven contoured sheets tend to slip off the corners of mattresses as the ends of such beds are raised and/or lowered.
Knitted contoured bed sheets avoid some of these problems as they inherently stretch to fit and hold better to various thicknesses and adjusted positions of mattresses, without the need for an elastic binding. But, knit fabrics are typically less durable and have a less desirable hand than woven fabrics. Moreover, knitted fabrics are more complicated and costly to process in commercial laundry as they are not easily handled with ordinary flat work ironers or folding machinery common in commercial laundry settings. As a result, knitted sheets tend to require more manual handling, and thus increase processing costs as compared to woven fabrics. Further, laundry efficiency is generally reduced by the need to handle both woven and knitted fabrics. Also, hybrid products combining both woven and knit fabrics have been introduced, but are not sufficient to meet the demands of the health care and hospitality markets.
The hospitality market tends to prefer woven fabrics and the healthcare market, while accepting of knitted fabrics, could also benefit from woven fabrics. To that end, attempts have been made to add stretch and recovery characteristics to woven fabric without requiring elastic binding around the edge. One proposal is to include spandex yarns or core-spun yarns along with the traditional, typically non-elastic yarns. But results have been considered unsatisfactory. For example, spandex based yarns tend to become discolored and degrade when exposed to chlorine and heat, both commonly encountered in commercial laundry settings. Core-spun yarns are undesirable because they lack durability in the institutional wash process and they limit the ability to control the elastomeric content in the fabric. Another proposal has been to induce a stretch characteristic into the sheet by treatments that affect the sinuosity and crimp of the yarns. However, the treatment process undesirably increases cost and often involves chemicals considered harmful to workers and the environment.